Diodes are employed in analog, mixed signal, and radio frequency (RF) semiconductor circuits for various purposes including power applications and wireless applications. A typical vertical p-n junction diode employs a vertical p-n junction formed by implantation of opposite types of dopants at different implantation depths. A typical Schottky barrier diode employs a vertical metal semiconductor junction that provides rectifying characteristics such as a junction between a metal silicide and a doped silicon portion. Vertical p-n junction diodes and Schottky barrier diodes are typically formed in a bulk semiconductor substrate since formation of a vertical p-n junction or a vertical Schottky barrier requires control of thicknesses of two different materials.
Formation of such diodes in a semiconductor-on-insulator (SOI) substrate poses a challenge since the thickness of a top semiconductor layer tends to be insufficient to allow formation of two vertical layers with precise thickness control. As the thickness of the top semiconductor layer decreases below 100 nm, and in many cases below 50 nm, implementation of conventional vertical diode such as a p-n junction diode and Schottky barrier diode becomes impractical due to the difficulty of forming a vertical junction in the top semiconductor layer. Further, shallow trench isolation structures in an SOI substrate contacts a buried insulator layer, and consequently, contact to a lower terminal of a vertical diode becomes difficult.
In addition, a Schottky barrier diode requires a doped guard ring to prevent excessive leakage current. Standard source/drain ion implantation, which may be employed to form a doped guard ring in a bulk substrate, does not provide an adequate structure for a doped guard ring since dopants from standard source/drain implantation reaches to the buried insulator layer in the case of the SOI substrate. Thus, no adequate method is provided for formation of a doped guard ring in an SOI substrate according to prior art methods.
In view of the above, there exists a need for a diode that may be manufactured in an SOI substrate despite a limited thickness of a top semiconductor layer, and methods of manufacturing the same.
Particularly, there exists a need for a Schottky barrier diode that may be manufacture in the SOI substrate with a functional doped guard ring to prevent excessive leakage current from the Schottky diode to the top semiconductor layer, and methods of manufacturing the same.